Systems operating on a refrigerant cycle, both refrigeration and heat pump systems, include a portion which expands a condensed liquid refrigerant from a relatively high condenser pressure to a relatively low evaporator pressure. This expansion commonly includes a partial evaporation of the refrigerant. Expansion valves, capillaries, float valves and orifices have been used for such expansion means. In the evaporator proper, the refrigerant evaporates, drawing heat of vaporization from a material to be cooled, such as circulating air, a secondary coolant such as glycol-water or the like. Precoolers are sometimes used to pass evaporated refrigerant coming out of the evaporator in heat exchange relation with condensed refrigerant prior to expansion. Such expansion and evaporation devices find application in many different refrigeration cycles, including standard compression and absorption cycles.